Abstract:

The disclosed is a dielectric ceramic composition in which dielectric
particles 2a are formed. The dielectric particle 2a has a core 22a
comprised of hexagonal barium titanate, and a shell 24a formed on an
outer circumference of the core 22a and comprised of cubical or
tetragonal barium titanate. The purpose of the present invention is to
provide a new dielectric ceramic composition, in which permittivity is
hardly lowered due to size effect, a good balance between high insulation
resistance and permittivity can easily be achieved, and changes in
insulation resistance and specific permittivity due to temperature are
small; and an electronic component such as a multilayer ceramic capacitor
using the dielectric ceramic composition as its dielectric layer.

Claims:

1. A dielectric ceramic composition in which dielectric particles are
formed, said dielectric particles comprising a core comprised of
hexagonal barium titanate, a shell formed on an outer circumference of
said core and comprised of cubical or tetragonal barium titanate.

2. The dielectric ceramic composition as set forth in claim 1, wherein
said hexagonal barium titanate is expressed by a general formula,
(Ba.sub.1-.alpha.M1.sub.α)A
(Ti.sub.1-.beta.M2.sub.β)BO3; an effective ionic radius of
said M1 is -20% or more to +20% or less with respect to an effective
ionic radius of 12-coordinated Ba2+; an effective ionic radius of
said M2 is -20% or more to +20% or less with respect to an effective
ionic radius of 6-coordinated Ti4+; and said A, B, α and
β satisfy the following relations: 0.900.ltoreq.(A/B)≦1.040,
0.ltoreq.α≦0.10 and 0.ltoreq.β≦0.2.

3. The dielectric ceramic composition as set forth in claim 2, wherein
said cubical or tetragonal barium titanate is different in crystal
structure from said hexagonal barium titanate but is expressed by said
general formula, (Ba.sub.1-.alpha.M1.sub.α)A
(Ti.sub.1-.beta.M2.sub.β)BO.sub.3.

4. The dielectric ceramic composition as set forth in claim 1, wherein a
grain boundary is formed between said dielectric particles, and additive
elements are dispersed in said grain boundary and/or said shell.

5. The dielectric ceramic composition as set forth in claim 2, wherein a
grain boundary is formed between said dielectric particles, and additive
elements are dispersed in said grain boundary and/or said shell.

6. The dielectric ceramic composition as set forth in claim 3, wherein a
grain boundary is formed between said dielectric particles, and additive
elements are dispersed in said grain boundary and/or said shell.

7. An electronic component having a dielectric layer, wherein said
dielectric layer is comprised of the dielectric ceramic composition as
set forth in claim 1.

8. An electronic component having a dielectric layer, wherein said
dielectric layer is comprised of the dielectric ceramic composition as
set forth in claim 2.

9. An electronic component having a dielectric layer, wherein said
dielectric layer is comprised of the dielectric ceramic composition as
set forth in claim 3.

10. An electronic component having a dielectric layer, wherein said
dielectric layer is comprised of the dielectric ceramic composition as
set forth in claim 4.

11. An electronic component having a dielectric layer, wherein said
dielectric layer is comprised of the dielectric ceramic composition as
set forth in claim 5.

12. An electronic component having a dielectric layer, wherein said
dielectric layer is comprised of the dielectric ceramic composition as
set forth in claim 6.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a new dielectric ceramic
composition and an electronic component such as a multilayer ceramic
capacitor in which the dielectric ceramic composition is used as its
dielectric layer.

[0003] 2. Description of the Related Art

[0004] Barium titanate is one of dielectric materials used in an
electronic component such as a capacitor. The barium titanate generally
has a tetragonal or cubical structure. Conventionally, it has been
possible to make layers thinner and to stack more layers by pulverization
of barium titanate, resulting in capacity expansion of the capacitor and
the like.

[0005] However, with pulverization of barium titanate, a phenomenon called
a size effect, in which permittivity of raw material itself is reduced,
has become more prominent, and become a major problem for future
development in electronic components.

[0006] Namely, in a tetragonal barium titanate, capacity expansion may not
be achievable by making layers thinner and stacking more layers as before
because permittivity can be lowered due to the size effect, and it is
therefore required to develop dielectric materials showing no size effect
or having small impact thereof.

[0007] As the dielectric material, a hexagonal barium titanate has
attracted attention, for instance. However, in the crystal structure of
barium titanate, the hexagonal structure is a metastable phase, and can
only exist normally at 1460° C. or more. Therefore, for obtaining
the hexagonal barium titanate at room temperature, it is necessary to
rapidly cool down from high temperature of 1460° C. or more.

[0008] Consequently, Nonpatent Literature 1, for example, discloses the
use of BaCO3, TiO2 and Mn3O4 as starting materials
and heat treatment thereof. This may allow lowering transformation
temperature to the hexagonal structure, so that it is possible to rapidly
cool down from a temperature of 1460° C. or less to obtain a
hexagonal barium titanate in which Mn is in solid solution state.

[0009] However, when actually using the hexagonal barium titanate obtained
by the method disclosed in the Nonpatent Literature 1 as a dielectric
layer of a capacitor, particle size constituting the dielectric layer may
be increased, so that it is difficult to use this for a multilayer
capacitor.

[0010] Note that the present inventors have proposed that permittivity can
be improved by adding La and the like to a hexagonal barium titanate.
However, the hexagonal barium titanate to which La and the like is added
shows reduction in insulation resistance and large change in specific
permittivity due to atmospheric temperature, and therefore, it is
unsuitable to use this without modification for an electronic component
such as a capacitor.

[0012] The present invention has been achieved in view of this situation,
and has purposes to provide a new dielectric ceramic composition, in
which permittivity is hardly lowered due to size effect, a good balance
between high insulation resistance and permittivity can easily be
achieved, and changes in insulation resistance and specific permittivity
due to temperature are small; and an electronic component such as a
multilayer ceramic capacitor in which the dielectric ceramic composition
is used as a dielectric layer.

[0013] To achieve the above purposes, in a dielectric ceramic composition
according to the present invention in which dielectric particles are
formed,

said dielectric particles comprise a core comprised of hexagonal barium
titanate, and a shell, formed on an outer circumference of said core and
comprised of cubical or tetragonal barium titanate.

[0014] The dielectric ceramic composition according to the present
invention comprises, instead of dielectric particles consisting only of
hexagonal barium titanate, dielectric particles including the core
comprised of hexagonal barium titanate and the shell comprised of cubical
or tetragonal barium titanate. The dielectric particles can be expected
to hardly lower permittivity even due to size effect because the core is
comprised of hexagonal barium titanate.

[0015] Also, the present inventors have confirmed that it is possible to
achieve a good balance between high insulation resistance and
permittivity by adopting a core shell structure such that the core
comprised of hexagonal barium titanate is coated with the shell comprised
of cubical or tetragonal barium titanate. In addition, it has been
confirmed that change in insulation resistance and specific permittivity
due to temperature can be reduced by adopting such a core shell
structure.

[0016] Preferably,

[0017] said hexagonal barium titanate is expressed by a general formula,
(Ba1-αM1.sub.α)A
(Ti1-βM2.sub.β)BO3;

[0018] an effective ionic radius of said M1 is -20% or more to +20% or
less (within ±20%) with respect to an effective ionic radius of
12-coordinated Ba2+;

[0019] an effective ionic radius of said M2 is -20% or more to +20% or
less (within ±20%) with respect to an effective ionic radius of
6-coordinated Ti4+; and

[0020] said A, B, α and β satisfy the following relations:
0.900≦(A/B)≦1.040, 0≦α≦0.1 and
0≦β≦0.2.

[0021] Preferably, said cubical or tetragonal barium titanate is different
in crystal structure from said hexagonal barium titanate but is expressed
by said general formula, (Ba1-αM1.sub.α)A
(Ti1-βM2.sub.β)BO3.

[0022] A grain boundary may be formed between said dielectric particles,
and additive elements may be dispersed in said grain boundary and/or said
shell.

[0023] The electronic component according to the present invention has a
dielectric layer comprised of any one of the above-described dielectric
ceramic compositions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a schematic sectional view of a multilayer ceramic
capacitor according to one embodiment of the present invention.

[0025] FIG. 2 is a sectional view of an enlarged key part of the
dielectric layer shown in FIG. 1.

[0026]FIG. 3 is a pattern of electron analysis of the core and the shell
in the core shell structure of the dielectric particle shown in FIG. 2,
measured by a transmission electron microscope.

[0027]FIG. 4 is a result of XRD measurement of the dielectric particle
shown in FIG. 2, a graph in which oxygen partial pressure at firing is
changed.

[0028] FIG. 5 is a conceptual diagram of the dielectric particle shown in
FIG. 2.

[0029]FIG. 6 is a graph showing a change in insulation resistance with
temperature of a dielectric ceramic composition according to Example 1 of
the present invention.

[0030]FIG. 7 is a graph showing a change in specific permittivity with
temperature of the dielectric ceramic composition according to Example 1
of the present invention.

[0031]FIG. 8 is a graph showing a change in insulation resistance with
temperature of a dielectric ceramic composition according to Example 3 of
the present invention.

[0032] FIG. 9 is a graph showing a change in specific permittivity with
temperature of the dielectric ceramic composition according to Example 3
of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereinafter, the present invention will be explained based on
embodiments shown in the drawings.

First Embodiment

[0034] The present embodiment will be explained by exemplifying a
multilayer ceramic capacitor 1 shown in FIG. 1 as an electronic
component, but the present invention is not necessarily limited to a
capacitor with stacking dielectric layers. Also, the present invention
can be applied to any other electronic components having a dielectric
layer as well as capacitors.

[0035] Multilayer Ceramic Capacitor

[0036] As shown in FIG. 1, the multilayer ceramic capacitor 1 as an
electronic component according to one embodiment of the present invention
has a capacitor element body 10 in which dielectric layers 2 and internal
electrode layers 3 are alternately stacked. At both ends of the capacitor
element body 10, a pair of external electrodes 4 is formed, which are
respectively conducted with internal electrode layers 3 alternately
arranged inside the element body 10. The internal electrode layers 3 are
stacked such that each end face is alternately exposed to surfaces of two
opposed ends of the capacitor element body 10. The pair of external
electrodes 4 is formed on both ends of the capacitor element body 10, and
connected to the exposed end face of the alternately arranged internal
electrode layers 3, constituting a capacitor circuit.

[0037] The outer shape and dimension of the capacitor element body 10 are
not particularly limited, and can be properly determined depending on the
intended use. Normally, the outer shape can be approximately rectangular
parallelepiped shape, and the dimension can normally be about (0.4 to 5.6
mm) in length, (0.2 to 5.0 mm) in width and (0.2 to 1.9 mm) in height.

[0038] Dielectric Layer

[0039] The dielectric layer 2 shown in FIG. 1 is constituted, as shown in
FIG. 2, to include a plurality of dielectric particles (crystal grains)
2a and grain boundaries 2b formed between pluralities of adjacent
dielectric particles 2a. The dielectric particle (crystal grain) 2a is
comprised of a core 22a, comprised of hexagonal barium titanate, and a
shell 24a, formed on an outer circumference of the core 22a and comprised
of cubical or tetragonal barium titanate.

[0040] In the present embodiment, a core shell structure of the dielectric
particle 2a means a structure in which the core 22a as a central portion
of the dielectric particle and the shell 24a coating the surface of the
core 22a are different in crystal structure but are integrated and have
approximately same composition. Note that "approximately same
composition" here means that some subcomponents may be dispersed in the
shell and that the core 22a and the shell 24a are somehow different in
compositions when more appropriate.

[0041] As shown in FIG. 3, as a result of electron analysis on the core
22a via measurement by a transmission electron microscope, a pattern
specific to hexagonal barium titanate can be observed, and as a result of
electron analysis on the shell 24a via measurement by the transmission
electron microscope, a pattern specific to tetragonal or cubical barium
titanate can be observed.

[0042] Also, when measuring an X-ray diffraction (XRD) pattern by
supposedly using an X-ray diffractometer for only a portion corresponding
to the core 22a of the dielectric particle 2a shown in FIG. 2, only a
peak specific to hexagonal barium titanate can come out as shown in solid
line in FIG. 4. It is difficult to measure only the portion corresponding
to the core 22a of the dielectric particle 2a shown in FIG. 2 with an
existing X-ray diffractometer while it is easy to measure an X-ray
diffraction (XRD) pattern for a part of the dielectric layer 2.

[0043] In case of such a measurement in the present embodiment, a peak
specific to cubical or tetragonal barium titanate can come out along with
the peak specific to hexagonal barium titanate as shown in dashed-dotted
line in FIG. 4. This can lead to assume that the dielectric particle
constituting the dielectric layer 2 according to the present embodiment
has the above-mentioned core shell structure.

[0044] In the present embodiment, the dielectric layer 2 is produced by
using raw powder as main component, which is comprised of hexagonal
barium titanate and contains almost no raw powder for cubical or
tetragonal barium titanate, adding subcomponent if required and firing,
as described below. Based on this, when there appear two peaks in the
measured XRD pattern as with the dashed-dotted line shown in FIG. 4, it
can be assumed that the dielectric particle 2a has the above-mentioned
core shell structure.

[0045] In the core shell structure of the present embodiment, it is not
necessary that the shell 24a completely coats whole circumference of the
core 22a, and the core 22a may partially be exposed. Based on this point
of view, as shown in FIG. 5, a maximum thickness "t1" in the shell 24a of
the dielectric particle 2a is more than 0 which is a thickness enough not
to eliminate the core 24a of the dielectric particle 2a, and a minimum
thickness "t2" may be 0.

[0046] In the core shell structure of the present embodiment, a boundary
of the core 22a and shell 24a is not necessarily definite, and at least,
the hexagonal barium titanate may exist close to the center of the
dielectric particle 2a while the cubical or tetragonal shell 24a may
exist near the surface (close to grain boundary).

[0047] Note that an average particle diameter "D50" (unit in gm) of the
whole dielectric particles 2a in the dielectric layer 2 can be defined as
a value obtained by cutting the capacitor element body 10 in a stacking
direction of the dielectric layer 2 and internal electrode layer 3,
measuring an average area of 200 or more of the dielectric particles 2a
in the cross-sectional surface shown in FIG. 2, and calculating a
diameter assuming that the particles are circular, followed by
multiplying the diameter by 1.5. In the present embodiment, the upper
limit of the average particle diameter "D50" of the whole dielectric
particles 2a can be the thickness of the dielectric layer 2, and "D50"
can be preferably 25% or less, more preferably 15% or less, of the
thickness of the dielectric layer 2.

[0048] The grain boundary 2b is normally composed of oxides of materials
constituting dielectric materials or internal electrode materials, oxides
of separately added materials, and oxides of materials contaminated as
impurities during the process.

[0049] In the present embodiment, the dielectric ceramic composition
forming the core 22a and shell 24a are not particularly limited, and can
preferably be constituted as below.

[0050] Namely, the core 22a in the dielectric layer 2 shown in FIG. 2 is
expressed by the following general formula,
(Ba1-αM1.sub.α)A
(Ti1-βM2.sub.β)BO3,

[0051] an effective ionic radius of the above M1 is -20% or more to +20%
or less (within ±20%) with respect to an effective ionic radius of
12-coordinated Ba2+;

[0052] an effective ionic radius of the above M2 is -20% or more to +20%
or less (within ±20%) with respect to an effective ionic radius of
6-coordinated Ti4+; and

[0053] the above A, B, α and β satisfy the following relations:
0.900≦(A/B)≦1.040, 0≦α≦0.1 and
0≦β≦0.2.

[0054] In the above general formula, α indicates a substitution
ratio of the element M1 to Ba (a content of M1 in the hexagonal-based
barium titanate powder). In the present embodiment, the capacitor 1 shown
in FIG. 1 can be used for temperature compensation, and is required to
show small changes in properties such as specific permittivity in a broad
temperature range, but the specific permittivity of the dielectric layer
2 may not necessarily be so high, Based on the point of view, in the
present embodiment, α satisfies preferably
0≦α<0.003, further preferably
0≦α≦0.002. A large content of M1 may result in higher
transformation temperature to the hexagonal structure, so that it tends
to be difficult to obtain powder having large specific surface as raw
powder.

[0055] Ba occupies a position of A site as Ba2+ in the hexagonal
structure. The element M1 is substituted for Ba to satisfy the above
range, and may exist at the position of A site, and the A site may be
occupied only by Ba. Namely, the element M1 may not be included in the
hexagonal barium titanate.

[0056] As mentioned above, the element M1 can preferably have the
effective ionic radius of -20% or more to +20% or less (within ±20%)
with respect to the effective ionic radius (1.61 pm) of 12-coordinated
Ba2+. Ba can easily be substituted with M1 because M1 has such an
effective ionic radius.

[0057] Specifically, the element M1 is preferably at least one selected
from Dy, Gd, Ho, Y, Er, Yb, La, Ce and Bi. The element M1 may be selected
depending on the desired properties, and preferably be La.

[0058] In the above general formula, β indicates a substitution ratio
of the element M2 to Ti (a content of M2 in the hexagonal-based barium
titanate powder), and β is preferably satisfies
0.03≦β≦0.20, further preferably
0.05≦β≦0.15 in the present embodiment. When the
content of the element M2 is either too low or too high, transformation
temperature to the hexagonal structure may be increased, so that it tends
not to obtain powder having large specific surface as raw powder.

[0059] Ti occupies a position of B site as Ti4+ in the hexagonal
structure. In the present embodiment, the element M2 is substituted for
Ti to satisfy the above range, and exists at the position of B site.
Namely, the element M2 is solid soluble in barium titanate. By the
existence of the element M2 at the position of B site, transformation
temperature from the tetragonal/cubical structure to the hexagonal
structure can be lowered in the barium titanate.

[0060] As mentioned above, the element M2 can preferably have the
effective ionic radius of -20% or more to +20% or less (within ±20%)
with respect to the effective ionic radius of 6-coordinated Ti4+. Ti
can easily be substituted with M1 because the element M2 has such an
effective ionic radius. As the element M2, Mn, Ga, Cr, Co, Fe, Ir and Ag
may be specifically exemplified, and preferably Mn.

[0061] The A and B in the above formula indicate a ratio of the elements
(Ba and M1) occupying A site and a ratio of the elements (Ti and M2)
occupying B site, respectively. In the present embodiment, A and B
preferably satisfy 1.000<A/B≦1.040, further preferably
1.006≦A/B≦1.036.

[0062] When A/B is too small, reactivity may be high at preparation of
barium titanate during the production of the raw powder, and grain growth
may easily occur with respect to temperature. Therefore, it may be
difficult to obtain fine powder, and the desired specific surface may
hardly be obtained. On the other hand, when A/B is too large, Ba-rich
orthobarium titanate (Ba2TiO4) may be generated as a
hetero-phase because the ratio of Ba is increased during the production
of the raw powder, which is not preferable.

[0063] The core 22a and shell 24a shown in FIG. 2 are different in crystal
structure, but the dielectric ceramic compositions thereof are
approximately same. Note that subcomponents included in the raw powder of
the dielectric ceramic composition may be dispersed in the shell 24a and
grain boundary 2b. As the subcomponents, for example, the following
compounds may be used. Note that the amount of oxygen (O) may be slightly
deviated from the stoichiometric composition in a variety of
compositional formulae of oxides shown below.

[0064] Namely, the subcomponents include:

[0065] at least one alkaline-earth oxide selected from a group consisting
of MgO, CaO and BaO,

[0066] at least one metal oxide selected from a group consisting of
Mn3O4 CuO, Cr2O3 and Al2O3,

[0067] at least one oxide of rare-earth selected from a group consisting
of Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Yb, and

[0068] glass component including SiO2.

[0069] The glass component including SiO2 is used as a sintering
auxiliary agent, and ZnO--B2O3--SiO2 glass,
B2O3--SiO2 glass, BaO--CaO--SiO2, SiO2 and the
like can preferably be used. The amount of the glass component is, in
terms of SiO2, preferably 0 to 5 parts by mole, further preferably
0.5 to 2 parts by mole, with respect to 100 parts by mole of the main
component including barium titanate expressed by the above-mentioned
general formula.

[0070] Amounts of other subcomponents except for the glass component are,
in terms of metal element, preferably 0 to 5 parts by mole, further
preferably 0.1 to 3 parts by mole, with respect to 100 parts by mole of
the main component including barium titanate expressed by the
above-mentioned general formula.

[0071] Note that the effective ionic radii in the present description are
based on the following literature: "R. D. Shannon, Acta Crystallogr., A
32,751(1976)".

[0072] Internal Electrode Layer

[0073] The internal electrode layer 3 shown in FIG. I can be constituted
by base-metal conducting material substantially working as an electrode.
For the base metal used as the conducting material, Ni or Ni alloy is
preferable. As the Ni alloy, an alloy of Ni with one or more elements
selected from Mn, Cr, Co, Al, Ru, Rh, Ta, Re, Os, Ir, Pt and W is
preferable, and Ni content in the alloy is preferably 95 wt % or more.
Note that a variety of minor components such as P, C, Nb, Fe, Cl, B, Li,
Na, K, F and S may be included at about 0.1 wt % or less in the Ni or Ni
alloy. In the present embodiment, the thickness of the internal electrode
layer 3 can be preferably less than 2 μm, more preferably 1.5 μm or
less, and thus, the internal electrode layer 3 is made thinner.

[0074] External Electrode

[0075] For the external electrode 4 shown in FIG. 1, normally, at least
one of Ni, Pd, Ag, Au, Cu, Pt, Rh, Ru and Ir or alloys thereof can be
used. Normally, Cu, Cu alloy, Ni or Ni alloy, Ag, Ag--Pd alloy, In--Ga
alloy and the like can be used. The thickness of the external electrode 4
may properly determined depending on the intended use, and normally
preferably 10 to 200 μm or so.

[0076] Production Method of Multilayer Ceramic Capacitor

[0077] First, a method for producing hexagonal-based barium titanate
powder will be explained, which is raw powder of the main component for
forming the dielectric layer 2 shown in FIG. 1. Initially, raw material
for barium titanate, and raw material for Mn as the element M2 are
prepared. Raw material for the element M1 may be prepared if required.

[0078] As the raw material for the barium titanate, barium titanate
(BaTiO3), oxides constituting barium titanate (BaO, TiO2) and
mixture thereof can be used. In addition, raw materials can be properly
selected from a variety of compounds to become the above-mentioned oxides
and composite oxide by firing, such as carbonate, oxalate, nitrate,
hydroxide and organic metal compound, and mixed together to use.
Specifically, as the raw material for the barium titanate, BaTiO3
may be used, and BaCO3 and TiO2 may be used. In the present
embodiment, it is preferable to use BaCO3 and TiO2.

[0079] Note that BaTiO3 used as the raw material for the barium
titanate may be barium titanate having a tetragonal structure, barium
titanate having a cubical structure, or barium titanate having a
hexagonal structure. Alternatively, mixture thereof may be used as well.

[0080] Also, as the raw material for M2, M2 compounds, such as oxide,
carbonate, oxalate, nitrate, hydroxide and organic metal compound, may be
properly selected and mixed to use. The raw material for the element M1
may be selected as with the raw material for M2.

[0081] Next, the prepared raw materials are weighed to have the
predetermined composition ratio, mixed and if required pulverized, so
that raw material mixture can be obtained. As a method for mixing and
pulverizing, for example, there may be mentioned a wet method in which
raw materials are thrown in a publicly-known pulverizer such as ball mill
along with a solvent such as water, and then mixed/pulverized. Also, by
using a dry method performed with a dry mixer and the like, the raw
materials may be mixed/pulverized. To improve the dispersibility of the
raw materials, it is preferable to add a dispersant. Publicly-known
dispersants may be used.

[0082] Then, the obtained raw material mixture is dried if required,
followed by heat treatment. Also, holding temperature in the heat
treatment may be set higher than transformation temperature to hexagonal
structure. In the present embodiment, the transformation temperature to
hexagonal structure is lower than 1460° C., and varies depending
on A/B, an amount of substitution at A site (α) and an amount of
substitution at B site (β) and the like, so that the holding
temperature may be changed depending on the change in transformation
temperature. To increase specific surface of powder, for example, it is
preferable to set at 1050 to 1250° C. The heat treatment may be
done under reduced pressure.

[0083] Such a heat treatment may allow obtaining solid solution of M2 in
BaTiO3 and substituting Ti at B site with M2. As a result, the
transformation temperature to hexagonal structure can be set lower than
the holding temperature at the heat treatment, so that hexagonal-based
barium titanate can easily be generated. Also, when the element M1 is
included, the element M1 can be included in BaTiO3 as a solid
solution and substituted for Ba at A site.

[0084] Then, after the elapse of holding time in the heat treatment, the
temperature can be lowered from the holding temperature in the heat
treatment to room temperature to maintain the hexagonal structure.
Specifically, the cooling rate is preferably set at 200° C./hour
or more.

[0085] This may allow obtaining hexagonal-based barium titanate powder
containing hexagonal barium titanate, in which the hexagonal structure is
maintained at room temperature, as a main component. A method for
evaluating whether the obtained powder is hexagonal-based barium titanate
powder or not is not particularly limited, and it is evaluated by X-ray
diffraction measurement in the present embodiment.

[0086] By using thus-obtained hexagonal-based barium titanate powder, an
electronic component having dielectric layers and electrode layers can be
produced. Specifically, the multilayer ceramic capacitor 1 shown in FIG.
1 can be produced as follows, for example. First, a dielectric paste
containing the hexagonal-based barium titanate powder according to the
present embodiment and an internal electrode layer paste are prepared,
and these are used to form a dielectric layer before firing and an
internal electrode layer before firing by doctor blade method and/or
printing method. An added amount of each raw material may be determined
so that the dielectric ceramic composition after firing has the
above-described constitution.

[0087] Next, a green chip is produced in which the dielectric layer before
firing and the internal electrode layer before firing are stacked,
followed by binder removal step, firing step, and if required, annealing
step, to form a sintered body. A capacitor element body 10 comprised of
the sintered body is then formed with an external electrode 4, so that
the multilayer ceramic capacitor 1 can be produced.

[0088] In the present embodiment, the atmosphere at firing is preferably
reduction atmosphere. For atmosphere gas in the reduction atmosphere, for
example, it is preferable to use humidified mixed gas of N2 and
H2. Oxygen partial pressure in the firing atmosphere is preferably
10-3 to 10-6 Pa. The reduction firing at the oxygen partial
pressure lower than the predetermined value may result in grain growth of
hexagonal barium titanate particle, included in the dielectric layer
before firing as the main component, by changing its surface to cubical
or tetragonal crystal, so that it is possible that the particle has the
above-mentioned core shell structure. Also, in the grain boundary and
shell after firing, subcomponents included in the dielectric layer before
firing are dispersed.

[0089] By controlling the oxygen partial pressure or firing temperature in
the firing atmosphere, it is possible to control average particle
diameter of the dielectric particle 2a constituting the dielectric layer
2 after firing, thickness of the shell 24a and the like. As shown in FIG.
4, by changing the oxygen partial pressure (PO2) from 10-2 to
10-8 which is strongly reduced atmosphere, a peak of cubical or
tetragonal crystal can be observed as well as a peak only of hexagonal
crystal in the X-ray diffraction (XRD) pattern. This may allow confirming
that it is possible to control cubical or tetragonal shell to be thick by
changing to strongly reduced atmosphere.

[0090] In the present embodiment, it is possible to combine insulation
resistance with high permittivity by adopting the core shell structure in
which the core 22a comprised of hexagonal barium titanate is covered with
the shell 24a comprised of cubical or tetragonal barium titanate. In
addition, by adopting the core shell structure, the change in specific
permittivity with temperature can be lowered.

[0091] Also, the core 22a in the dielectric ceramic composition
constituting the dielectric layer 2 of the multilayer ceramic capacitor
according to the present embodiment has a constitution where the amount
of substitution with the element M1 is 0 or small while the amount of
substitution with the element M2 is relatively large in the hexagonal
barium titanate expressed by (Ba1-αM1.sub.α)A
(Ti1-βM2.sub.β)BO3. Therefore, compared to the
constitution where the amount of substitution with the element M2 is 0 or
small while the amount of substitution with the element M1 is large,
permittivity is inferior but change rate in permittivity with temperature
is small, and change rate in insulation resistance with temperature is
also small. Consequently, the multilayer ceramic capacitor 1 of the
present embodiment can preferably be used as a temperature compensation
capacitor.

Second Embodiment

[0092] In the second embodiment, except for changing the constitutions of
the core 22a and shell 24a in the dielectric particle 2a shown in FIG. 2
from those in the first embodiment, a sample can be prepared as in the
first embodiment, and its specific permittivity of the dielectric layer 2
is remarkably improved.

[0093] Namely, in the present embodiment, the core 22a in the dielectric
layer 2 shown in FIG. 2 is, as in the first embodiment, hexagonal barium
titanate expressed by the general formula,
(Ba1-αM1.sub.α)A
(T1-βM2.sub.β)BO3 but is different in its ranges
of A, B, α and β from those in the first embodiment. Note that
the shell 24a has approximately same constitution with the core 22a but
is different in crystal structure as in the first embodiment. Also, as in
the first embodiment, the shell 24a is comprised of tetragonal or cubical
barium titanate and subcomponents may be dispersed in the shell 24a and
grain boundary 2b.

[0094] In the above general formula, to remarkably improve specific
permittivity of the dielectric ceramic composition, the ranges of A, B,
α and β are set as follows in the present embodiment.

[0095] Namely, a satisfies a relation of 0<α≦0.10,
preferably 0.003≦α≦0.05. When α is small, M1
content may be decreased, and it may become difficult to remarkably
improve specific permittivity. In contrast, when M1 content is too large,
transformation temperature to hexagonal structure at the production of
raw powder may be increased, and it tends to be hard to obtain powder
having large specific surface.

[0096] Also, in the present embodiment, A and B satisfy a relation of
0.900≦A/B≦1.040, preferably 0.958≦A/B≦1.036.
Furthermore, β satisfies a relation of 0≦β≦0.2,
preferably 0.03≦β≦0.20, further preferably
0.03≦β≦0.10. When M2 content is 0 or small, specific
permittivity can remarkably be improved, but it tends to be hard to
produce raw powder of the hexagonal barium titanate because
transformation temperature to hexagonal structure may be increased at the
production of the raw powder.

[0097] In the present embodiment, it is possible to combine insulation
resistance with high permittivity by adopting the core shell structure in
which the core 22a comprised of hexagonal barium titanate is coated with
the shell 24a comprised of cubical or tetragonal barium titanate. In
addition, by adopting the core shell structure, the change in specific
permittivity with temperature can be lowered.

[0098] Also, the core 22a in the dielectric ceramic composition
constituting the dielectric layer 2 of the multilayer ceramic capacitor
according to the present embodiment has a constitution where the amount
of substitution with the element M1 is relatively high while the amount
of substitution with the element M2 is 0 or relatively low in the
hexagonal barium titanate expressed by
(Ba1-αM1.sub.α)A
(Ti1-βM2.sub.β)BO3. Therefore, compared to the
first embodiment, permittivity may be remarkably improved, the change
rate in permittivity with temperature may be small, and the change rate
in insulation resistance with temperature may also be small.

[0099] Note that the present invention is not limited to the
above-described embodiments, and can be variously modified within the
range of the present invention.

[0100] For example, in the above embodiments, the core shell structure is
achieved in the dielectric particle 2a constituting the dielectric layer
2 after firing by controlling the oxygen partial pressure and firing
temperature in the firing atmosphere when firing the element body 10.
However, the core shell structure may be achieved in the dielectric
particle 2a constituting the dielectric layer 2 after firing by selecting
conditions for calcining hexagonal barium titanate particles.

[0101] Also, in the above embodiments, the multilayer ceramic capacitor is
exemplified as the electronic component according to the present
invention, but the electronic component according to the present
invention is not limited to the multilayer ceramic capacitor, and may be
any of those having a dielectric layer comprised of a dielectric ceramic
composition having a dielectric particle with the above-described core
shell structure.

EXAMPLES

[0102] Hereinafter, the present invention will be explained based on
further detailed examples, but the present invention is not limited to
these examples. Note that in the following examples, "specific
permittivity ε" and "insulation resistance IR" were measured as
below.

[0103] (Specific Permittivity ε and Insulation Resistance)

[0104] For a capacitor sample, capacitance C was measured at reference
temperature 20° C. under conditions with frequency of 1 kHz and
level of input signal (measured voltage) of 0.5 Vrms/pm by using a
digital LCR meter (YHP4274A by Yokogawa Electric Corporation). From
thus-obtained capacitance, a thickness of a dielectric body of a
multilayer ceramic capacitor and an overlapped area of internal
electrodes, specific permittivity (no unit) was calculated.

[0105] Then, after DC50V was applied to the capacitor sample by using an
insulation resistance tester (R8340A by Advantest Corporation) at
25° C. for 60 seconds, insulation resistance IR was measured.

Example 1

[0106] First, raw powder of main component and raw powder of subcomponent
were prepared. For the raw powder of main component, hexagonal barium
titanate powder expressed by the general formula,
(Ba1-αM1.sub.α)A
(Ti1-βM2.sub.β)BO3 where α=0, β=0.15,
M2=Mn and A/B=1, was used. The hexagonal barium titanate powder was
produced through solid-phase synthesis by using BaCO3 (specific
surface: 25 m2/g), TiO2 (specific surface: 50 m2/g) and
Mn3O4 (specific surface: 20 m2/g).

[0107] As a result of X-ray diffraction of the obtained hexagonal-based
barium titanate powder, it was possible to confirm the obtained powder
was hexagonal-based barium titanate powder. Also, as a result of
measuring specific surface by BET method, a specific surface by BET
method of the obtained hexagonal-based barium titanate powder was 5
m2/g.

[0108] With respect to 100 parts by mole of the hexagonal barium titanate
powder, 1 part by mole of ZnO--B2O3--SiO2 glass in terms
of SiO2 and 1 part by mole of an oxide of at least one rare-earth
element selected from a group consisting of Y, Gd and Dy in terms of
metal element were prepared. These were added with polyvinyl butyral
resin and ethanol-based organic solvent, and mixed with a ball mill to
form a paste, so that a dielectric layer paste was obtained.

[0109] Next, 100 parts by weight of Ni particle, 40 parts by weight of
organic vehicle (in which 8 parts by weight of ethylcellulose was
dissolved in 92 parts by weight of butyl carbitol) and 10 parts by weight
of butyl carbitol were kneaded by triple-roll to form a paste, so that an
internal electrode layer paste was obtained.

[0110] Also separately, 100 parts by weight of Cu particle, 35 parts by
weight of organic vehicle (in which 8 parts by weight of ethylcellulose
resin was dissolved in 92 parts by weight of butyl carbitol) and 7 parts
by weight of butyl carbitol were kneaded to form a paste, so that an
external electrode paste was obtained.

[0111] Then, a green sheet with a thickness of 2.5 μm was formed on PET
film by using the above dielectric layer paste and the internal electrode
layer paste was printed on the green sheet, followed by removal of the
green sheet from the PET film. Next, the green sheet and protective green
sheet (on which no internal electrode layer paste was printed) were
stacked and thermocompressively bonded to obtain a green laminate. The
number of layers of the sheets having internal electrodes was 100.

[0112] The green chip was then cut in a predetermined size, followed by
binder removal treatment, firing and annealing in the following
conditions, so that a sintered chip was obtained. The conditions for the
binder removal treatment included holding temperature of 260° C.
and atmosphere of in air. The firing condition included holding
temperature of 1000° C. The atmosphere gas was humidified mixed
gas of N2+H2, and was reducing gas in which oxygen partial
pressure of the atmosphere gas was 1×10-8 Pa. For the anneal
conditions, normal conditions were employed,

[0113] Then, end faces of the fired multilayer ceramic body were polished
by sandblast, followed by transferring the external electrode paste onto
the end faces and firing in humidified N2+H2 atmosphere at
900° C. to form external electrodes, so that a multilayer ceramic
capacitor sample having a structure shown in FIG. 1 was obtained. Next,
Sn plated layer and Ni plated layer were formed on the external electrode
surface to obtain a sample for measurements.

[0114] The size of each of thus-obtained samples was 3.2 mm×1.6
mm×1.6 mm, the number of the dielectric layers sandwiched between
the internal electrode layers was 100, and the thickness of the internal
electrode layer was 2 μm. As a result of measuring X-ray diffraction
(XRD) pattern for the dielectric layer by using X-ray diffractometer, the
peak specific to cubical or tetragonal barium titanate was observed as
well as the peak specific to hexagonal barium titanate, as shown by the
dashed-dotted line shown in FIG. 4.

[0115] Also, as shown in FIG. 3, when the core 22a was measured by a
transmission electron microscope for electron analysis, the pattern
specific to hexagonal barium titanate was observed while the pattern
specific to tetragonal or cubical barium titanate was observed when the
shell 24a was measured by the transmission electron microscope for
electron analysis. Namely, it was confirmed that the particles had the
core shell structure.

[0116] Furthermore, for the obtained capacitor sample for the present
example, insulation resistance and specific permittivity were evaluated.
The results are shown by the dotted line "ex. 1" in FIG. 6 and FIG. 7.

Example 2

[0117] Except for changing the oxygen partial pressure at firing to
10-4 Pa, a capacitor sample was produced as with Example 1, and the
measurements were done in the same procedures. When measuring X-ray
diffraction (XRD) pattern for the dielectric layer by using X-ray
diffractometer, the peak specific to cubical or tetragonal barium
titanate was observed as well as the peak specific to hexagonal barium
titanate, as shown by the dashed line shown in FIG. 4. Note that the peak
specific to cubical or tetragonal barium titanate was low compared to
Example 1. From this result, it was confirmed that the thickness of the
shell 24a comprised of cubical or tetragonal barium titanate as shown in
FIG. 2 was controllable.

Comparative Example 1

[0118] Except for changing the oxygen partial pressure at firing to
10-1 Pa, a capacitor sample was produced as with Example 1, and the
measurements were done in the same procedures. As a result of
measurements of X-ray diffraction (XRD) pattern for the dielectric layer
by using X-ray diffractometer, only the peak specific to hexagonal barium
titanate was observed. From this result, it was confirmed that the
dielectric layer was formed by hexagonal barium titanate particle, in
which the shell as shown in FIG. 2 was not formed, and grain boundary.
For the obtained capacitor sample for the comparative example, insulation
resistance and specific permittivity were evaluated. The results are
shown by the solid line "cex. 1" in FIG. 6 and FIG. 7.

Comparative Example 2

[0119] Except for using tetragonal barium titanate powder as raw powder of
the main component, a capacitor sample was produced and specific
permittivity was measured, as with Example 1. The results are shown by
the dashed line "cex. 2" in FIG. 7.

Evaluation 1

[0120] As shown in FIG. 6 and FIG. 7, it was confirmed in Example 1 (ex.
1) that insulation resistance was improved as well as specific
permittivity while changes in properties with temperature were small,
compared to Comparative Example 1 (cex. 1). It was also confirmed in
Example (ex. 1) that changes in properties with temperature were
considerably small, while permittivity was lowered in whole, compared to
Comparative Example 2 (cex. 2).

Example 3

[0121] For the raw powder of the main component, hexagonal barium titanate
powder expressed by the general formula,
(Ba1-αM1.sub.α)A
(Ti1-βM2.sub.β)BO3 where α=0.003,
β=0, M1=La and A/B=1.04, was used. Except for producing the
hexagonal barium titanate powder by using BaCO3 (specific surface:
25 m2/g), TiO2 (specific surface: 50 m2/g) and
La(OH)3 (specific surface: 20 m2/g) under reduced pressure via
solid-phase synthesis, a capacitor sample was produced as with Example 1,
and the measurements were done in the same procedures as with Example 1.

[0122] Namely, as a result of measurement of X-ray diffraction (XRD)
pattern for the dielectric layer by using X-ray diffractometer, the peak
specific to cubical or tetragonal barium titanate was observed as well as
the peak specific to hexagonal barium titanate, as shown by the
dashed-dotted line shown in FIG. 4.

[0123] Also, as shown in FIG. 3, when the core 22a was measured by the
transmission electron microscope for electron analysis, the pattern
specific to hexagonal barium titanate was observed while the pattern
specific to tetragonal or cubical barium titanate was observed when the
shell 24a was measured by the transmission electron microscope for
electron analysis. Namely, it was confirmed that the particles had the
core shell structure.

[0124] Furthermore, for the obtained capacitor sample of the present
example, insulation resistance and specific permittivity were evaluated.
The results are shown by the dashed line "ex. 3" in FIG. 8 and FIG. 9.

Comparative Example 3

[0125] Except for changing the oxygen partial pressure at firing to
10-1 Pa, a capacitor sample was produced as with Example 3, and the
measurements were done in the same procedures. As a result of measurement
of X-ray diffraction (XRD) pattern for the dielectric layer by using
X-ray diffractometer, only the peak specific to hexagonal barium titanate
was observed. From this result, it was confirmed that the dielectric
layer was formed by hexagonal barium titanate particle, in which the
shell as shown in FIG. 2 was not formed, and grain boundary. For the
obtained capacitor sample for the comparative example, insulation
resistance and specific permittivity were evaluated. The results are
shown by the solid line "cex. 3" in FIG. 8 and FIG. 9.

Evaluation 2

[0126] As shown in FIG. 8 and FIG. 9, it was confirmed in Example 3 (ex.
3) that insulation resistance was improved and changes in both specific
permittivity and insulation resistance with temperature were small while
specific permittivity was lowered, compared to Comparative Example 3
(cex. 3). It was also confirmed in Example 3 that specific permittivity
was considerably improved compared to Example 1.

Example 4

[0127] Except for using any one of Dy, Gd, Ho, Y, Er, Yb, Ce and Bi
instead of La as the element M1, a capacitor sample was produced as with
Example 3, the measurements were done in the same procedures, and it was
confirmed that the similar results were obtained as with Example 3. This
may be because these elements have an effective ionic radius of -20% or
more to +20% or less with respect to an effective ionic radius of
12-coordinated Ba2+, and are substituted for Ba, as with La.

Example 5

[0128] Except for setting M2=Mn and 0<β≦0.2, a capacitor
sample was produced as with Example 3, the measurements were done in the
same procedures, and it was confirmed that the similar results were
obtained as with Example 3. It was confirmed that properties can be
improved in ease of particularly 0.03≦β≦0.2, further
preferably 0.03≦β≦0.1.

Example 6

[0129] Except for using any one of Ga, Cr, Co, Fe, Ir and Ag instead of Mn
as the element M2, a capacitor sample was produced as with Example 5, the
measurements were done in the same procedures, and it was confirmed that
the similar results were obtained as with Example 5. This may be because
these elements have an effective ionic radius of -20% or more to +20% or
less with respect to an effective ionic radius of 6-coordinated
Ti4+, and are substituted for Ti, as with Mn.

Example 7

[0130] Except for setting 0.900≦A/B<1.04 as A/B, a capacitor
sample was produced as with Example 3, the measurements were done in the
same procedures, and it was confirmed that the similar results were
obtained as with Example 3.

Example 8

[0131] Except for using any one of Ga, Cr, Co, Fe, Ir and Ag instead of Mn
as the element M2, a capacitor sample was produced as with Example 1, the
measurements were done in the same procedures, and it was confirmed that
the similar results were obtained as with Example 1. This may be because
these elements have an effective ionic radius of -20% or more to +20% or
less with respect to the effective ionic radius of 6-coordinated
Ti4+, and are substituted for Ti, as with Mn.

Example 9

[0132] Except for setting M1=La and 0<α≦0.1, a capacitor
sample was produced as with Example 1, the measurements were done in the
same procedures, and it was confirmed that the similar results were
obtained as with Example 1. It was confirmed that properties can be
improved particularly in case of 0<α≦0.003.

Example 10

[0133] Except for using any one of Dy, Gd, Ho, Y, Er, Yb, Ce and Bi
instead of La as the element M1, a capacitor sample was produced as with
Example 9, the measurements were done in the same procedures, and it was
confirmed that the similar results were obtained as with Example 9.

Example 11

[0134] Except for changing β in the range of
0.003≦α≦0.2 but excluding 0.15, a capacitor sample
was produced as with Example 1, the measurements were done in the same
procedures, and it was confirmed that the similar results were obtained
as with Example 1.

Example 12

[0135] Except for changing A/B in the range of
0.900≦A/B≦1.04 but excluding 1.000, a capacitor sample was
produced as with Example 1, the measurements were done in the same
procedures, and it was confirmed that the similar results were obtained
as with Example 1.

Example 13

[0136] Except for forming tetragonal shell by adding tetragonal
BaTiO3 as an additive instead of changing oxygen partial pressure at
firing, a capacitor sample was produced as with Example 1, and the
measurements were done in the same procedures. As a result of measurement
of X-ray diffraction (XRD) pattern for the dielectric layer by using
X-ray diffractometer, it was confirmed that the peak specific to cubical
or tetragonal barium titanate can be displaced by changing an amount
added of the tetragonal BaTiO3 and that it is possible to control
the core shell, as with Example 1, Example 2 and Comparative Example 1
shown in FIG. 4.